Undecided questions,,Ich weiss'' und ,,wiess''

I have seen, or heard, in a few films German speakers will sometimes drop the "ich" from this sentence, or the sentence "Ich weiss nicht''. Is this common? It was "das Boot", or that was one of the films. Or, you know, is it current speech? Sie verstehen...

Answers

Sometimes they omit the verb too. I think it is also practiced in English.Example: "keine Ahnung" (no idea). It should be "ich habe keine Ahnung".Guten Tag (ich wünsche Ihnen einen guten Tag) is another example.